Year	Years
1970	1.46
1971	1.5
1972	1.54
1973	1.58
1974	1.63
1975	1.67
1976	1.72
1977	1.76
1978	1.81
1979	1.86
1980	1.91
1981	1.97
1982	2.02
1983	2.07
1984	2.13
1985	2.19
1986	2.25
1987	2.31
1988	2.37
1989	2.44
1990	2.51
1991	2.57
1992	2.64
1993	2.72
1994	2.79
1995	2.87
1996	2.95
1997	3.04
1998	3.12
1999	3.21
2000	3.3
2001	3.39
2002	3.48
2003	3.57
2004	3.66
2005	3.75
2006	3.85
2007	3.94
2008	4.04
2009	4.14
2010	4.24
2011	4.33
2012	4.44
2013	4.54
2014	4.64
2015	4.75